Bioactive glasses have been known for nearly 40 years and are considered osteoinductive and osteoconductive. They are currently used in a variety of bone repair and regeneration applications since these glasses react in a favorable way with the bodily fluids to form a calcium phosphate compound known as hydroxyapatite (HA) or carbonated hydroxyapatite (HCA). Since HA or HCA is the mineral component of natural bone, bioactive glasses form a strong chemical bond to human bone and over a period of time they are considered to be remodeled by the body to form new bone.
Silicate-based glasses have been used as a basis for implantable compositions to support the bonding, growth or genesis of bone by fostering a supportive environment between the material and living, bone progenitor cells. It is widely recognized that successful bioactive glasses include calcium and silica in order to foster the needed supportive environment. Certain of these compositions are considered bioactive since they possess surfaces capable of fostering a calcium phosphate layer which, in turn, promotes bone bonding to the material. For example, U.S. Pat. No. 5,204,106 discloses a composition termed 45S5 glass which is composed of Na2O—CaO—P2O5—SiO2.
Day et al. U.S. Pat. No. 6,709,744 describes biocompatible materials for implantation which include borate-based glass or ceramic materials containing Na2O, CaO, P2O5, and B2O3. A specific example is a glass containing about 22.9 wt % Na2O, about 22.9 wt % CaO, about 5.6 wt % P2O5, and about 48.6 wt % B2O3. These materials contain a high CaO concentration to facilitate the formation of hydroxyapatite when exposed to phosphorus-containing fluids in vivo or prior to implantation.
There is a continuing need for a wider variety of biocompatible materials which promote rapid repair of mammalian tissue.